fordfan25

08-02-2005, 07:27 PM

i understand the resoning but the numbers are what has me confused. wich would be a better P2W

18.6 or 17.3

what does the numbers reprosent?

18.6 or 17.3

what does the numbers reprosent?

View Full Version : please help me understand Power To Weight Ratio.

fordfan25

08-02-2005, 07:27 PM

i understand the resoning but the numbers are what has me confused. wich would be a better P2W

18.6 or 17.3

what does the numbers reprosent?

18.6 or 17.3

what does the numbers reprosent?

ytareh

08-02-2005, 07:40 PM

Imagine a 1000hp car that weighed 1000(pounds/kilos it doesnt matter.It would have a power to weight ratio of 1(1000 divided by 1000=1).Now imagine a 1000hp car that weighs 2000.Obviously its slower...Its power to weight ratio is 1000 divided by 2000 which is a half or 0.5.So the bigger the power to weight ratio the more lively the car/truck/plane is likely to be...The numbers themselves depend on the units used in the calculation.Once you are comparing like with like they dont really matter.Obviously if you use horsepower as the power unit(europeans might use KiloWatts...)when calculating the power to weight ratio of two cars but measure the weight of one in tons and the other in ounces the figures arent gonna be a fair comparison...(or tell you much).

BaldieJr

08-02-2005, 08:01 PM

Higher = better.

Unless, of course, the plane handles like a feathered boulder. Then all the power in the world wont amount to much more than "hovering target".

Unless, of course, the plane handles like a feathered boulder. Then all the power in the world wont amount to much more than "hovering target".

fordfan25

08-02-2005, 08:32 PM

Originally posted by ytareh:

Imagine a 1000hp car that weighed 1000(pounds/kilos it doesnt matter.It would have a power to weight ratio of 1(1000 divided by 1000=1).Now imagine a 1000hp car that weighs 2000.Obviously its slower...Its power to weight ratio is 1000 divided by 2000 which is a half or 0.5.So the bigger the power to weight ratio the more lively the car/truck/plane is likely to be...The numbers themselves depend on the units used in the calculation.Once you are comparing like with like they dont really matter.Obviously if you use horsepower as the power unit(europeans might use KiloWatts...)when calculating the power to weight ratio of two cars but measure the weight of one in tons and the other in ounces the figures arent gonna be a fair comparison...(or tell you much).

ok im still haveing trouble. so a 1000hpcar that ways 1000lb would be 1.1? and a 1000hp car that wighs 2000 would be 1.5 right?

so in the numbers i listed above say both are masured in HP and LB wich is better? 18.6 or 17.3?

Imagine a 1000hp car that weighed 1000(pounds/kilos it doesnt matter.It would have a power to weight ratio of 1(1000 divided by 1000=1).Now imagine a 1000hp car that weighs 2000.Obviously its slower...Its power to weight ratio is 1000 divided by 2000 which is a half or 0.5.So the bigger the power to weight ratio the more lively the car/truck/plane is likely to be...The numbers themselves depend on the units used in the calculation.Once you are comparing like with like they dont really matter.Obviously if you use horsepower as the power unit(europeans might use KiloWatts...)when calculating the power to weight ratio of two cars but measure the weight of one in tons and the other in ounces the figures arent gonna be a fair comparison...(or tell you much).

ok im still haveing trouble. so a 1000hpcar that ways 1000lb would be 1.1? and a 1000hp car that wighs 2000 would be 1.5 right?

so in the numbers i listed above say both are masured in HP and LB wich is better? 18.6 or 17.3?

FritzGryphon

08-02-2005, 08:34 PM

In my experience, this is usually expressed as 'power loading'. kg/kW or lbs/hp. Lower numbers would be better.

Your examples 18.6 and 17.3 could not be hp/lb, because it'd be way too high (imagine a P-47 with 250,000 hp).

18.6lb/hp for a 9000lb plane would mean 500hp motor.

What planes do these values belong to?

Your examples 18.6 and 17.3 could not be hp/lb, because it'd be way too high (imagine a P-47 with 250,000 hp).

18.6lb/hp for a 9000lb plane would mean 500hp motor.

What planes do these values belong to?

fordfan25

08-02-2005, 08:42 PM

Originally posted by FritzGryphon:

In my experience, this is usually expressed as 'power loading'. kg/kW or lbs/hp. Lower numbers would be better.

Your examples 18.6 and 17.3 could not be hp/lb, because it'd be way too high (imagine a P-47 with 250,000 hp).

18.6lb/hp for a 9000lb plane would mean 500hp motor.

What planes do these values belong to?

ill see if i can find a example. just a quick qustion would calculations like that take into acount of torge?

o and thay dont belong to any plane i just remember seeing them on a car sight. i just keep seeing P2W in discussions and i was wanting to get a better idea of how it worked out

In my experience, this is usually expressed as 'power loading'. kg/kW or lbs/hp. Lower numbers would be better.

Your examples 18.6 and 17.3 could not be hp/lb, because it'd be way too high (imagine a P-47 with 250,000 hp).

18.6lb/hp for a 9000lb plane would mean 500hp motor.

What planes do these values belong to?

ill see if i can find a example. just a quick qustion would calculations like that take into acount of torge?

o and thay dont belong to any plane i just remember seeing them on a car sight. i just keep seeing P2W in discussions and i was wanting to get a better idea of how it worked out

FritzGryphon

08-02-2005, 08:43 PM

I don't see why torque would be a factor. Airplanes are propelled by thrust, torque is just an unwanted side effect.

Of course it would with cars, but I don't know anything about that. (torque/weight?)

Of course it would with cars, but I don't know anything about that. (torque/weight?)

Tully__

08-02-2005, 08:47 PM

Originally posted by fordfan25:

i understand the resoning but the numbers are what has me confused. wich would be a better P2W

18.6 or 17.3

what does the numbers reprosent?

Do you mean "18.6 or 17.3" or "18:6 or 17:3". There is a HUGE difference.

The first is read "18 point 6 or 17 point 3". Provided both figures are in the same power to weight units (hp per pound or kilowatts per kilogram) the first figure is better.

The second is read "18 to 6 or 17 to 3". In this case, the second ratio is better, as the first works out to 3 power units per weight unit and the second is just under 6 power units per weight unit.

ok im still haveing trouble. so a 1000hpcar that ways 1000lb would be 1.1? and a 1000hp car that wighs 2000 would be 1. right? Wrong.

Using the first notation described above, 1000hp and 1000lbs would be expressed 1.0 hp/lb, 1000hp and 2000lbs would be expressed 0.5 hp/lb.

The figure is derived by dividing the Power by the Weight.

Using the ratio notation, 1000hp and 1000lbs would be written 1 hp:1 lb, 1000hp and 2000lbs would be written 1 hp:2 lb

In terms of what it means, the more hp for each lb, the better the acceleration.

If the figure is epressed as power loading as mentioned by FritzGryphon, you want a lower number. The less pounds each hp has to push around, the better the acceleration.

i understand the resoning but the numbers are what has me confused. wich would be a better P2W

18.6 or 17.3

what does the numbers reprosent?

Do you mean "18.6 or 17.3" or "18:6 or 17:3". There is a HUGE difference.

The first is read "18 point 6 or 17 point 3". Provided both figures are in the same power to weight units (hp per pound or kilowatts per kilogram) the first figure is better.

The second is read "18 to 6 or 17 to 3". In this case, the second ratio is better, as the first works out to 3 power units per weight unit and the second is just under 6 power units per weight unit.

ok im still haveing trouble. so a 1000hpcar that ways 1000lb would be 1.1? and a 1000hp car that wighs 2000 would be 1. right? Wrong.

Using the first notation described above, 1000hp and 1000lbs would be expressed 1.0 hp/lb, 1000hp and 2000lbs would be expressed 0.5 hp/lb.

The figure is derived by dividing the Power by the Weight.

Using the ratio notation, 1000hp and 1000lbs would be written 1 hp:1 lb, 1000hp and 2000lbs would be written 1 hp:2 lb

In terms of what it means, the more hp for each lb, the better the acceleration.

If the figure is epressed as power loading as mentioned by FritzGryphon, you want a lower number. The less pounds each hp has to push around, the better the acceleration.

XyZspineZyX

08-02-2005, 08:50 PM

simply put, a 1000 lb car witha 1000 hp motor would have the motor pull 1 lb per horsepower, in other words, if you wanna get the power to weight ratio, divide the weight of the a/c to the horsepower of the motor, youll get the amount of horsepower required per lb of airplane

Tully__

08-02-2005, 08:57 PM

Originally posted by FritzGryphon:

I don't see why torque would be a factor. Airplanes are propelled by thrust, torque is just an unwanted side effect.

Of course it would with cars, but I don't know anything about that. (torque/weight?)

The torque characteristics of an engine affects how the engine feels to fly and how versatile the engine is. It is also important when working out best cruise rpm, as piston engines tend to be most efficient when operating at or near the rpm where they make the most torque.

It should also be noted that power is basically (torque@rpm) x rpm.

I don't see why torque would be a factor. Airplanes are propelled by thrust, torque is just an unwanted side effect.

Of course it would with cars, but I don't know anything about that. (torque/weight?)

The torque characteristics of an engine affects how the engine feels to fly and how versatile the engine is. It is also important when working out best cruise rpm, as piston engines tend to be most efficient when operating at or near the rpm where they make the most torque.

It should also be noted that power is basically (torque@rpm) x rpm.

JG7_Rall

08-02-2005, 09:01 PM

numbers dont mean much without units. That'll clear a lot of this up if you provide the units. kthx

fordfan25

08-02-2005, 09:02 PM

Originally posted by FritzGryphon:

I don't see why torque would be a factor. Airplanes are propelled by thrust, torque is just an unwanted side effect.

Of course it would with cars, but I don't know anything about that. (torque/weight?)

o right. yea that would be true. good thing i dont disign piston fighters.*ford* whats wrong with you people theres not enough torgue here! i want more torgue* lol i feel sory for the test piolet of my fighter LMAO. just cranking her up would cause the thing to flip over lol.

I don't see why torque would be a factor. Airplanes are propelled by thrust, torque is just an unwanted side effect.

Of course it would with cars, but I don't know anything about that. (torque/weight?)

o right. yea that would be true. good thing i dont disign piston fighters.*ford* whats wrong with you people theres not enough torgue here! i want more torgue* lol i feel sory for the test piolet of my fighter LMAO. just cranking her up would cause the thing to flip over lol.

fordfan25

08-02-2005, 09:21 PM

never mind i got it i think http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif.

thanks for the help. but now my brain feels kinda funny http://forums.ubi.com/images/smilies/blink.gif

thanks for the help. but now my brain feels kinda funny http://forums.ubi.com/images/smilies/blink.gif

Oilburner_TAW

08-02-2005, 09:56 PM

If your comparing 2 vehicles/planes,whatever the units mean nothing as long as both are using the same units (ie hp/lb). Power to weight ratio is just that..

Power divided by weight. 2000hp in a 1000lb car would be expressed as 2000 divided by 1000 = 2 (think of it as 2/1).

So, for every 2 hp there is 1lb of weight

A 1000hp in a 3000lb car would be 1000 divided by 3000, = .333 (think of it as 1/3).

So, for every 1 hp there is 3lbs of weight.

Power divided by weight. 2000hp in a 1000lb car would be expressed as 2000 divided by 1000 = 2 (think of it as 2/1).

So, for every 2 hp there is 1lb of weight

A 1000hp in a 3000lb car would be 1000 divided by 3000, = .333 (think of it as 1/3).

So, for every 1 hp there is 3lbs of weight.